1. Field of the Invention
This invention relates to a magnetic head, and more particularly, to a magnetic head comprising a magnetic core fixed in a case by using a fixing material comprising a plurality of epoxy resins having different number of epoxy groups from each other.
2. Description of the Prior Art
An ordinary magnetic head is as illustrated in FIG. 1 which is a front view of the magnetic head and in FIG. 2 which is a cross sectional view of the magnetic head of FIG. 1 taken along the dot and dash line A--A', and the cross section is viewed from the upper portion of FIG. 1.
In FIG. 1 and FIG. 2, reference numeral 1 denotes a core, 2 a case, 3 a fixing material, 4 a gap, 5 a spacer, 6 an intercepting plate, 7 a coil, 8 a terminal and 9 a sliding surface.
Degradation of electromagnetic converting characteristic is attributable to the following cause.
That is, fixing material 3 fixes core 1 (magnetic core) composed of a material of high permeability into case 2, but the difference in coefficient of linear expansion between fixing material 3 and the core results in a shrinking stress against core 1 when fixing material 3 is cured and shrinks.
After using the magnetic head for a long time after fixing material 3 is cured, fixing material 3 absorbs moisture in air. As a result, fixing material 3 is deformed and a stepwise difference is formed in the vicinity of gap 4, and therefore, a tape (not shown) can not closely contact sliding surface 9 of the head and the recording characteristics and reproduction characteristics are degraded.
For the purpose of decreasing such degradation of the electromagnetic converting characteristic, it is necessary to use a fixing material of low coefficient of linear expansion and low boiling water absorption. For the purpose of obtaining such fixing material, a certain amount of a filler, for example, calcium carbonate, silica, talc or a mixture thereof is added.
The above mentioned boiling water absorption is determined according to JIS (Japanese Industrial Standard) K6911-1979, 5.27, as shown below.